By 1967, King had become the country's most prominent opponent of the Vietnam War, and a staunch critic of overall U.S. foreign policy, which he deemed militaristic. In his "Beyond Vietnam" speech delivered at New York's Riverside Church on April 4, 1967 -- a year to the day before he was murdered -- King called the United States "the greatest purveyor of violence in the world today."

Time magazine called the speech "demagogic slander that sounded like a script for Radio Hanoi," and the Washington Post declared that King had "diminished his usefulness to his cause, his country, his people."